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Also, the derived perturbation potential parameters ǫ1 , ǫ2 and ǫ3 are found to be comparable. 2). This is in contrast to the field galaxies where A1 and A2 are comparable and are generally stronger than A3 and the other higher mode amplitudes (Rix & Zaritsky 1995). This indicates the importance of multiple, simultaneous tidal interactions that can occur under the special conditions of a group environment. This needs to be studied by future dynamical studies including by N-body simulations. 5Mpc/300 km s−1 ∼ 3Gyr, the long-term maintenance of lopsidedness is not a problem in this environment.

The typical dynamical friction time-scale, for an object of mass M at about 10pc from the center, in a spiral galaxy with a bulge of ∼ 1010 M⊙ , typical of an Sb galaxy like M31, is ∼ 107 (106 M⊙ /M) yr, and it could be much smaller inside. Although short with respect to galactic time-scales, this is much larger than the orbital time of 3 ×105 yr at this radius. Tremaine et al (1975) precisely proposed that the central stellar nuclei in spiral galaxies are 45 the results of many globular clusters infalling by dynamical friction.

Fig. 15. NGC data - near-IR data (left panel), and the same from N-body simulations with gas accretion in two streamers at a rate so as to double the mass of the galaxy in a Hubble time (right panel), taken from Bournaud et al. (2005 b). A word of caution is that if gas accretion is the mechanism for generation of lopsidedness, one would expect to see asymmetry in the gas velocity fields whereas these are smoothly continuous as pointed out by Baldwin et al. (1980). 2 for the details. Other physical models have also been developed in the literature but these are probably not as widely applicable due to the specific parameters or conditions chosen, as discussed below.

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Lopsided Spiral Galaxies - C. Jog, F. Combes [preprint]

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